Electrochemical reforming of oxygenate mixtures

ABSTRACT

The process describes performing electrolysis on an alkaline oxygenate mixture to produce hydrogen. In this process the electrolysis does not form any significant amounts of oxygen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application which claims the benefit of and priority to U.S. Provisional Application Ser. No. 61/715,971 filed Oct. 19, 2012, entitled “Electrochemical Reforming of Oxygenate Mixtures”, which is hereby incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

FIELD OF THE INVENTION

This invention relates to electrochemical reforming of oxygenate mixtures.

BACKGROUND OF THE INVENTION

Hydrogen is currently produced by steam-reforming of natural gas. This process although economical, produces CO₂ as a by-product. With increasing demand for hydrogen in refineries, and the possibility of future carbon dioxide legislation, it is of interest to consider cost-effective alternative means of H₂ production. The electrochemical splitting of water into H₂ and O₂ gas is one known method. However, electrolysis requires electrical power, which either means significant CO₂ emission from coal-based power, or reliance on the development of economical sources of low-carbon power.

At the same time there is all increased need to utilize higher amounts of biomass. Biomass is known as a renewable energy source that can be used to manufacture transportation fuel. However, manufacture of transportation fuel from biomass requires H₂. While steam-reforming of natural gas call provide the required H₂, but it adds to the CO₂ footprint of the process. There exists a need to efficiently produce H₂ while decreasing the amount of CO₂ produced.

BRIEF SUMMARY OF THE DISCLOSURE

The process describes performing electrolysis on an alkaline oxygenate mixture to produce hydrogen. In this process the electrolysis does not form any significant amounts of oxygen.

In another embodiment the process describes alkalinizing an oxygenate mixture to produce an alkaline oxygenate mixture. Electrolysis is performed on the alkaline oxygenate mixture to produce hydrogen. In this process the electrolysis does not form any significant amounts of oxygen.

In yet another embodiment the process describes continuously alkalinizing an oxygenate mixture comprising a biomass or a biomass derived stream. Electrolysis is then conducted with a platinum or a platinum alloy blend anode and cathode at temperatures greater than 150° C., pressures greater than 200 psig and at an applied voltage less than 1.23 volts to produce hydrogen. In this process the electrolysis does not form any significant amounts of oxygen or carbon dioxide and the current density during electrolysis is greater than 15 mA/cm².

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and benefits thereof may he acquired by referring to the follow description taken in conjunction with the accompanying drawings in which:

FIG. 1 depicts a schematic of a corn fiber/stover to fuels process.

FIG. 2 depicts a schematic for algae processing.

FIG. 3 depicts a cyclic voltammogram for electrolysis of corn fiber oxygenates.

FIG. 4 depicts a cyclic voltammogram for electrolysis of cellulosic oxygenates.

FIG. 5 depicts current density from alternating current electrolysis of cellulosic oxygenates.

FIG. 6 depicts a cyclic voltammogram for electrolysis of algal oxygenates.

FIG. 7 depicts a cyclic voltammogram for electrolysis of lignin oxygenates.

FIG. 8 depicts current density from alternating current electrolysis of lignin oxygenates.

FIG. 9 depicts a cyclic voltammogram for electrolysis of lignin polymer in an acidic and alkaline environment.

FIG. 10 depicts cyclic voltammogram for electrolysis of lignin oxygenates with Pt alloy catalysts.

FIG. 11 depicts current density from alternating current electrolysis of lignin oxygenates.

FIG. 12 depicts current density from alternating current electrolysis of lignin oxygenates over a wider range of temperatures.

DETAILED DESCRIPTION

Turning now to the detailed description of the preferred arrangement or arrangements of the present invention, it should be understood that the inventive features and concepts may be manifested in other arrangements and that the scope of the invention is not limited to the embodiments described or illustrated. The scope of the invention is intended only to be limited by the scope of the claims that follow.

The process describes performing electrolysis on an alkaline oxygenate mixture to produce hydrogen. In this process the electrolysis does not form any significant amounts of oxygen.

Oxygenated chemical compounds are chemicals that contain oxygen as part of their chemical structure. In one embodiment, the oxygenates used in this process can be from any biomass or biomass derived stream. As an example different sources of the oxygenates include corn fiber/stover derived aqueous streams, lignin, lignocellulosic biomass, and algae.

In one embodiment the oxygenates are corn fiber/stover derived organic streams. FIG. 1 depicts one possible schematic of the COM fiber/stover to fuels process. Corn fiber, separated from the corn kernel in a wet mill, is hydrolyzed in the presence of acids (dilute H₂SO₄) to produce sugar monomers. These sugar monomers are separated and cleaned through several stages and hydrogenated and converted to C₅ and C₆ sugar alcohols. These sugar alcohols (dissolved in water) are then further upgraded to a hydrocarbon mixture using hydrotreating technology. During hydrotreating, oxygen is removed as water. This water along with the feed water constitutes as the biomass derived stream.

The broad spectrum of organics contained in that derived stream includes oxygenates, many of which can be oxidized electrochemically more easily than water can. Alcohols, esters, ketones, carboxylic acids, sugars and sugar dehydration products are notable in this respect. Sugars and alcohols can be oxidized electrochemically more easily than water earl. A sugar/alcohol-water mixture therefore contains one species that is easily reduced but difficult to oxidize (water), and a different species that is easily oxidized but difficult to reduce (sugars/alcohols). Electrolysis of the mixture therefore produces hydrogen at one electrode from the reduction of water, and oxidized organic waste at the other electrode. Meanwhile the overall reaction is thermodynamically more favorable in energy than either the electrolysis of water in the absence of the organics or vice versa. The organics are not generally oxidized all the way to carbon dioxide but are instead converted selectively into carboxylic acids.

In another embodiment the oxygenates are lignin. Lignin is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. Lignin can be oxidized electrochemically more easily than water can. A lignin-water mixture therefore contains one species that is easily reduced but difficult to oxidize (water), and a different species that is easily oxidized but difficult to reduce (lignin). Electrolysis of the mixture therefore produces hydrogen at one electrode from the reduction of water, and oxidized products at the other electrode. Meanwhile the overall reaction is thermodynamically more favorable in energy than either the electrolysis of water in the absence of the organics or vice versa.

One method of preparing the lignin for this process is through a biomass pyrolysis process. In this non-limiting example red oak (wood) biomass was pyrolyzed at 450° C. Heavy pyrolysis oil (boiling point >180° F.) was collected by cooling pyrolysis vapors and washed with distilled water at around a 1:1 ratio. The aqueous phase (primarily sugars) was decanted, leaving behind the water-insoluble (phenol oligomers/lignin) at a water content around 10-15 wt %. The lignin/phenol oligomers were produced as residual material from the water extraction of pyrolysis oil. No additional chemical treatment was required. While this approach is described as a method for obtaining residual lignin it may work for other oxygenates such as corn stover or grasses. The availability of the feedstock is therefore only limited by the logistics of growing, harvesting, and transporting the biomass. unconverted lignin can account for up to 15-30 wt % of the biomass feed, providing significant amounts for conversion to hydrogen.

In another embodiment the oxygenates are lignocellulosic biomass (cellulose, hemicellulose, and lignin). Lignocellulosic biomasses are a low-value feedstock that can be obtained as a by-product from agricultural and biofuels processes. Cellulose and hemicellulose are polymers of sugar molecules which can either be upgraded to fuels or reformed to produce hydrogen. Lignin is a polymer of complex phenolic groups and accounts for about 15-30% of the biomass weight. In order to convert the biomass to hydrogen, the biomass needs to be first broken down to simpler molecules. For example, art aqueous mixture of organics is known to oxidize more readily than water.

Cellulose can he oxidized electrochemically more easily than water can. A cellulose-water mixture therefore contains one species that is easily reduced but difficult to oxidize (water), and a different species that is easily oxidized but difficult to reduce (cellulose). Electrolysis of the mixture therefore produces hydrogen at one electrode from the reduction of water, and oxidized products at the other electrode. Meanwhile the overall reaction is thermodynamically more favorable in energy than either the electrolysis of water in the absence of the organics or vice versa.

In yet another embodiment algae residue can be used as the oxygenates. Algae residue is typically made up of carbohydrates such as cellulose, proteins and ash. These can be oxidized electrochemically more easily than water can. A residue-water mixture therefore contains one species that is easily reduced but difficult to oxidize (water), and a different species that is easily oxidized but difficult to reduce (algae residue). Electrolysis of the mixture therefore produces hydrogen at one electrode from the reduction of water, and oxidized products at the other electrode. Meanwhile the overall reaction is theorized to be thermodynamically more favorable, in energy that either the electrolysis of water in the absence of the cellulose or vice versa. FIG. 2 shows one possible schematic for algae processing to lipids and the eventual electrochemical reforming of the residue for hydrogen production.

In this non-limiting example algae of Nannochloropsis gaditana species were grown in artificial sea water media. The ponds were harvested using a continuous centrifuge. The culture was pumped into the centrifuge at a flow-rate of 600 ml/min and centrifuged at a rotor speed of 6000 rpm. The algae pellets obtained, from harvesting were used for iso-propanol lipid extraction. A solution of algae and iso-propanol was made in such a way that the final concentration of iso-propanol was 70% and the final amount of algae in the solution was 15%. This solution was poured into a round-bottom flask and refluxed for 1 hour at 80° C. The refluxed sample was then vacuum-filtered. The filtrate was dried to remove the iso-propanol from the crude lipids. The solids from the filtering step were washed again with 70% iso-propanol and filtered again. The solids were dried in an oven (105° C.) for 12 hours, The filtrate from the second was dried to remove the iso-propanol from the crude lipids to form the algae residue after the extraction of the lipids. The crude lipids in iso-propanol are then ready to he electrochemically reformed.

In the process, the oxygenate mixture can be alkalinized with any known alkaline salt. The alkaline solutions can be made from any known alkali metal or alkaline earth metal, Non-limiting examples of common alkaline solutions that can be used include NaOH. KOH, Ca(OH)₂, Mg(OH)₂, NH₄OH, Na₂CO₃, and Na₂SiO₃. In one embodiment from about 1 wt % to about 35 wt % of the alkaline oxygenate mixture can he an alkaline electrolyte. In another embodiment the alkaline oxygenate mixture contains from about 20 wt % to about 30 wt % of an alkaline electrolyte. Alternatively, one could view the alkaline oxygenate mixture as containing from about 1 wt % to about 80 wt % oxygenate, or even from about 5 wt % to about 40 wt % oxygenate.

The process of alkalinizing the oxygenate mixture can occur by any conventionally known method. This process can either occur either in a continuous manner or a batch reaction. In one embodiment the alkalinization and electrolysis is performed continuously.

Typical electrolysis occurs when an electrical power source is connected to two electrodes which are placed in water with supporting electrolyte present. The electrolysis for this process can occur as either a batch system or a continuous manner. Additionally, electrolysis in this process can occur with either an alternating current (AC) or a direct current (DC). It is theorized that by performing the electrolysis with alternating current the process can reduce the amount of fouling that can occur at the electrodes.

The selection of the anode electrode and the cathode electrode for this process can be any conductive metal or a conductive metal alloy. Non-limiting examples of anode or cathode materials that can be used include a group 4, 5, 6, 7, 8, 9, 10, 11 or 12 conductive metal and conductive metal alloys. Non-limiting specific examples of conductive metal or conductive metal alloys that can be used include, platinum and platinum alloy blends, palladium and palladium alloy blends, nickel and nickel alloy blends, iron and iron alloy blends, titanium and titanium alloy blends, gold and gold alloy blends. These anode and cathode materials are deposited on an electrically conductive substrate preferably carbon-based materials.

Although the electrolysis can occur at any range of temperatures the electrolysis of this process typically occurs at temperatures greater than 100° C. or even greater than 150° C. The pressure of the electrolysis typically occurs at pressures greater than atmospheric pressure or even greater than 200 psig. In one embodiment the electrolysis occurs at pressures from about 200 psig to about 400 psig.

In one embodiment of the current process the electrolysis occurs with an applied voltage less than 1.23 volts.

Using the different electrolytes, electrodes and reaction conditions described above. the current density of the electrolysis For this process ranges from. about 15 mA/cm² to about 400 mA/cm² or even from about 100 mA/cm² to about 350 mA/cm². If one were to perform the electrolysis at temperatures below 100° C. the current density of the electrolysis is greater than 15 mA/cm².

In one embodiment the electrolysis does not form any significant amounts of oxygen. Significant amounts of oxygen can be defined as any amount more than 33% mol of oxygen. In other terms significant amounts of oxygen can be defined as any amount more than 1.00 ppm of oxygen or ever 10 ppm of oxygen. In sonic embodiments no oxygen is formed by the electrolysis.

In one embodiment the electrolysis does not form any significant amounts of carbon dioxide. Significant amounts of carbon dioxide can be defined as any amount more than 500 ppm of carbon dioxide.

Examples Corn Fiber Oxygenate as Feed

Electrochemical tests were performed using samples of aqueous oxygenate stream of a corn fiber upgrading process. Ammonium hydroxide was added in a 0.5 M concentration as an alkaline electrolyte. Twin platinum plates were used as electrodes and held at a distance of 2 centimeters apart. Cyclic voltammograms were performed that show an enhanced onset of hydrogen evolution, resulting in a 17% reduction in the applied voltage when compared to pure water electrolysis. The cyclic voltammogram showing this difference is depicted in FIG. 3. Using an applied voltage of 1.5 volts between the two electrodes, a 35% increase yield. in H₂ production was also observed.

Although not specific to the corn fiber feed, the electrolysis process also has an additional benefit by removing alcohols, such as methanol, from biomass derived streams before they reach the treatment facility. Typically, microbes are used at treatment facilities to digest the organic content in the biomass derived streams. However, spikes in alcohol concentration in these streams are known to render the microbes ineffective. By removing the alcohols by electrolysis, the current process provides a better control over the biological oxygen demand and chemical oxygen demand. It also provides the refinery with flexibility to process various economic crudes with small amounts of alcohol in them. In different embodiments the electrolysis can remove 50%, 70%, 90%, 95%, even 99% of the alcohol in the biomass derived streams.

Cellulose Oxygenate as Feed

Electrolysis was performed using a 1-10 wt % corn stover cellulose in alkaline conditions. In this example KOH was used as the alkaline electrolyte. Samples of cellulose were suspended in the electrolyte and heated to 80° C. for an hour to allow the dissolution of sugars in the aqueous phase. Following the extraction of sugars, the insoluble solids were filtered out and disposed. An Au—Pt catalyst was electrochemically deposited on Ni foam and used both as the anode and cathode, The anode and catalyst were held at a distance of 1 cm apart from each other. FIG. 4 depicts cyclic voltammograms demonstrating the overall hydrogen generation in this system using 1% cellulose, 5% cellulose, 10% cellulose and 30% KOH in water.

As shown in the cyclic voltammogram higher or lower cellulose concentration result in lower current densities or hydrogen rates. FIG. 5 depicts current density from short-term tests conducted at 1.2 volts. In this test it is shown that 5% cellulose results in higher current densities than 10% cellulose.

Algae Oxygenate as Feed

Electrochemical tests were performed using 5-10 wt % of algae residue in alkaline conditions. Around 30 wt % of KOH was used as the alkaline electrolyte. Samples of the residue were suspended in the electrolyte and heated to 80° C. for an hour to allow the dissolution of the organics in the aqueous phase. Following the extraction of the sugars, proteins and the sort, the insoluble solids were filtered out and disposed. An Au—Pt catalyst was electrochemically deposited on Ni foam and used both as the anode and cathode. The anode and catalyst were held at a distance of 1 cm apart from each other. FIG. 6 depicts cyclic voltammograms demonstrating the overall hydrogen generation in this system using 5% algae, 10% algae and 30% KOH in water.

Lignin Oxygenate as Feed

Electrolysis was performed using 5 wt % lignin in both acidic and alkaline electrolytes. 30 wt % H₂SO₄ and 30 wt % KOH were used as electrolytes for the acidic and alkaline media respectively. An Au—Pt catalyst was electrochemically deposited on Ni foam and used as the anode, held at a distance of 1 cm apart from a Pt cathode. A base cyclic voltammogram of 30 wt % KOH in water was taken for comparison.

As shown in FIG. 7, a cyclic voltammogram demonstrates the comparison between electrolysis of 5 wt % of lignin polymer (powder), 5 wt % of lignin wood (semi-solid) and water, all with 30 wt % of KOH. As shown in this figure addition of the lignin wood results in a 40% reduction in applied voltage.

FIG. 8 depicts the resulting current density (200 mA/cm²) from alternating current electrolysis of the lignin wood conducted at 1.2 volts. Applying an alternating current decreases fouling of the electrodes and results in an increased hydrogen production rate.

FIG. 9 depicts that a cyclic voltammogram of the overall hydrogen generation of lignin polymer in acidic (H₂SO₄) and alkaline (KOH) media. As shown in the figure, hydrogen generation in enhanced under alkaline conditions.

FIG. 10 depicts cyclic voltammograms demonstrating the overall hydrogen generation in this system using 5% lignin, 10% lignin, 20% lignin and 30% wt. KOH in water. 10 wt. % lignin produced a higher current density than other lignin concentrations.

FIG. 11 depicts a current density of 400 mA/cm² from alternating current electrolysis conducted at 1.2 volts with 5% (red) and 10% (blue) lignin in 30% KOH electrolyte. Applying an alternating current decreases fouling of the electrodes and results in an increased hydrogen production rate.

FIG. 12 depicts the resulting current density from alternating current electrolysis conducted at a frequency of 25 Hz at varying voltages with 10% pyrolysis red oak lignin in 30% KOH electrolyte with NiPtAu₃ electrodes on expanded graphite substrates at different temperatures. Each data point was collected for 10 minutes.

In closing, it should be noted that the discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication date after the priority date of this application. At the same time, each and every claim below is hereby incorporated into this detailed description or specification as an additional embodiment of the present invention.

Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Those skilled in the art may be able to study the preferred embodiments and identify other ways to practice the invention that are not exactly as described herein. It is the intent of the inventors that variations and equivalents of the invention are within the scope of the claims while the description, abstract and drawings are not to be used to limit the scope of the invention. The invention is specifically intended to be as broad as the claims below and their equivalents. 

1. A process comprising: performing electrolysis on an alkaline oxygenate mixture to produce hydrogen, wherein the electrolysis does not form any significant amounts of oxygen.
 2. The process of claim 1, wherein the electrolysis forms less than 33% mol of oxygen.
 3. The process of claim 1, wherein the electrolysis forms less than 100 ppm of oxygen.
 4. The process of claim 1, wherein the alkaline oxygenate mixture is produced from biomass or a biomass derived stream.
 5. The process of claim 1, wherein the electrolysis occurs with either an alternating or a direct voltage or current.
 6. The process of claim 1, wherein the electrolysis occurs with an alternating voltage or current.
 7. The process of claim 1, wherein the alkaline oxygenate mixture contains from about 1 wt % to about 80 wt % oxygenate.
 8. The process of claim 1, wherein the alkaline oxygenate mixture contains from about 5 wt % to about 40 wt % oxygenate.
 9. The process of claim 1, wherein the alkaline oxygenate mixture contains from about 1 wt % to about 35 wt % of an alkaline electrolyte.
 10. The process of claim 1, wherein the alkaline oxygenate mixture contains from about 20 wt % to about 30 wt % of an alkaline electrolyte.
 11. The process of claim 1, wherein the current density of the electrolysis ranges from about 15 mA/cm² to about 400 mA/cm².
 12. The process of claim 1, wherein the current density of the electrolysis ranges from about 50 mA/cm² to about 350 mA/cm².
 13. The process of claim 1, wherein the anode comprises a conductive metal or a conductive metal alloy.
 14. The process of claim 1, wherein the anode comprises a conductive metal or a conductive metal alloy of a group 4, 5, 6, 7, 8,9, 10, 11 or 12 metal.
 15. The process of claim 1, wherein the anode comprises a conductive metal or a conductive metal alloy of the group comprising: platinum, palladium, gold, nickel and combinations thereof.
 16. The process of claim 1, wherein the anode is supported on a carbon-based material.
 17. The process of claim 1, wherein the cathode comprises a conductive metal or a conductive metal alloy.
 18. The process of claim 1, wherein the cathode comprises a conductive metal or a conductive metal alloy of a group 4, 5, 6, 7, 8, 9, 10, 11 or 12 metal.
 19. The process of claim 1, wherein the cathode comprises a conductive metal or a conductive metal alloy of the group comprising: platinum, palladium, gold, nickel and combinations thereof.
 20. The process of claim 1, wherein the cathode is supported on a carbon-based material.
 21. The process of claim 1, wherein the electrolysis does not form any significant amounts of carbon dioxide.
 22. The process of claim 1, wherein the electrolysis forms less than 500 ppm of carbon dioxide.
 23. The process of claim 1, wherein the current density of the electrolysis is greater than 15 mA/cm² at temperatures below 100° C.
 24. The process of claim 1, wherein the electrolysis occurs at temperatures greater than 100° C.
 25. The process of claim 1, wherein the electrolysis occurs at temperatures greater than 150° C.
 26. The process of claim 1, wherein the electrolysis occurs at pressures greater than atmospheric pressure.
 27. The process of claim 1, wherein the electrolysis occurs at pressures greater than 200 psig.
 28. The process of claim 1, wherein the electrolysis occurs at an applied voltage less than 1.23 volts.
 29. The process of claim 1, wherein the electrolysis occurs in a continuous manner.
 30. A process comprising: alkalinizing an oxygenate mixture to produce an alkaline oxygenate mixture; and performing electrolysis on the alkaline oxygenate mixture to produce hydrogen, wherein the electrolysis does not form any significant amounts of oxygen.
 31. The process of claim 30, wherein the alkaline oxygenate mixture is alkalinized and electrolyzed continuously.
 32. The process of claim 30, wherein the oxygenate mixture comprises of biomass or a biomass derived stream.
 33. A process comprising: continuously alkalinizing an oxygenate mixture, comprising, a biomass of a biomass derived stream; and performing electrolysis with an anode and a cathode comprising a conductive metal or a conductive metal alloy of the group comprising: platinum, palladium, gold, nickel and combinations thereof, wherein the anode and the cathode are supported on carbon-based materials and the electrolysis occurs at temperatures greater than 150° C., pressures greater than 200 psig and at an applied voltage less than 1.23 volts to produce hydrogen, wherein the electrolysis does not form does not form any significant amounts of oxygen or carbon dioxide and the current density of the electrolysis is greater than 15 mA/cm². 